Problem: William ate 2 slices of cake. Umaima ate 4 slices. If William ate $\dfrac{2}{7}$ of the cake, what fraction of the cake is remaining?
Solution: If 2 slices represent $\dfrac{2}{7}$ of the cake, there must have been a total of 7 slices. $\text{fraction of cake remaining} = \dfrac{\text{number of slices remaining}}{\text{number of slices total}}$ Together they ate 6 slices, which leaves 1 out of 7 slices remaining. There is $\dfrac{1}{7}$ of the cake remaining.